Posted
by
samzenpus
on Thursday July 03, 2014 @05:38PM
from the hit-the-lights dept.

KentuckyFC writes Stars form when clouds of gas and dust collapse under their own gravity, generating enough heat and pressure to fuse the atoms inside them together. When this cloud of dust and gas is the remnants of a supernova, it can contain all kinds of heavy elements in addition to primordial hydrogen, helium and lithium. Now one astrophysicist has calculated that a recently discovered phenomenon of turbulence, called preferential concentration, can profoundly alter star formation. He points out that turbulence is essentially vortices rotating on many scales of time and space. On certain scales, the inertial forces these eddies create can push heavy particles into the calmer space between the vortices, thereby increasing their concentration. In giant clouds of interstellar gas, this concentrates heavy elements, increasing their gravitational field, attracting more mass and so on. The result is the formation of a star that is made entirely of heavy elements rather than primordial ones. Astrophysicists call the amount of heavy elements in a star its "metallicity". Including preferential concentration in the standard model of star formation leads to the prediction that 1 in 10,000 stars should be totally metal. Now the race is on to find the first of this new class of entirely metal stars.

No, no, no. His stardom has finally reached the magnitude that it has become observable in outer space, by astrophysicists. Given his take on Shakespeare, [youtube.com] I doubt he'd make a good astrophysicist.

If you read the article, however, it would point out that astronomers use a skewed definition of "metal", as any element heavier than lithium.

At birth, stars contain little helium, but is is constantly generated by fusing hydrogen.

If you start with metals like sodium and potassium, plus what we normally call non-metals, like carbon and oxygen, then you won't get around to generating helium until you fuze something radioactive that emits an alpha particle.

Stellar fusion can occur with atomic elements up to iron. There are a number of metals that are lighter than iron. If I'm reading this right, stellar fusion could conceivably be triggered by heavier metallic elements if they were "selected for" by the properties of vortices during the formation process.

Additionally, in astrophysics the term "metal" includes many elements which are not metals in any other field. Astrophysically, metals are any element other than hydrogen or helium, so in addition to ordinary metals like sodium and lithium non-metallic elements such as carbon and oxygen are counted as metals.

To be clear, there are some varying definitions out there from anything other than hydrogen to anything other than hydrogen, helium, or lithium. Other than hydrogen and helium is the definition I've run across most often.

2. Not entirely. There are planets without stars, and there are stars which orbit stars (well, stars which orbit a barycentre between itself and another star, which may or may not be inside the other star).

No, they really are not. Gravity has very little effect at the atomic level, but at the level of solar systems is the primary force.

No, they might very well be. But it is just speculation --- accomplished science neither shows
whether they are or not. It's just speculation, either way.

Iif you subscribe to the Bohr model of an atom... our solar systems are a larger scale universe's atoms, then the force we call "Gravity" could be the larger scale universe's electromagnetic force, and then Earth

Huh? It's been demonstrated many times in many different ways that gravity is by far the weakest of the fundamental interactions. Gravity makes little difference at the atomic and subatomic levels. Atoms are not mini-solar systems. The forces that bind atomic nuclei and bind electrons to atomic nuclei are fundamentally different from gravity. Here's a tip; at least at the temperatures and densities you will find virtually everywhere in the universe today; gravity, electromagnetism, the strong and weak inter

To see someone making a claim that atoms are mini solar systems in the 21st century isn't too far different from someone claiming the Sun orbits the Earth.

You're either a nasty troll, or you just aren't paying attention at all. The claim was not that atoms are mini solar systems: quite the opposite; that our solar systems themselves are subatomic particles at a grander superscale: a superscale at which our entire solar system weighs something like 3 × 10^-29 grams.
And the passage of time from

Let's take TFA at face value, and assume one in 10k stars start their evolution as count as "metallic" stars.

Hydrogen main sequence stars burn for a a few million years (for the class O supergiants) to literally trillions of years (for the class M all-but-failures). Helium burning, in a star with sufficient mass, lasts between a few hundred thousand to a few dozen million years.

The subject of TFA starts after helium burning normally finishes - Next on a typical star comes carbon, lasting for only a few hundred years; Then comes neon lasting for a single year, oxygen at half a year, and silicon finishes its run in a single day.

So whether or not a star begins life with a high concentration of trans-lithium metals, it will have a very, very short lifetime; That one-in-ten-thousand creation ratio therefore reduces to more like one-in-a-trillion among those stars still shining in our nighttime sky.

I know very little of astronomy, but I have to wonder at the reason why each of the fusion cyles is shorter... is it only because some intrinsic property of the heavier fuel? I had alsways assumed that the fact that there is only a fraction of the original star mass that makes it to Carbon, and only a fraction of that to each successive element in the list what the root cause the the exponential decay in life expectancy of each fuel source. If that is the case, the reason that each cycle is shorter is the l

Fusion of hydrogen into helium produces a LOT of energy. Fusion of helium into carbon produces less. In physics terms, it's the "packing fraction" curve, which can show you what energy you'd get out if you fuse elements together.

Iron is at the bottom of the packing fraction curve; when you fuse other stuff into iron, you're getting out the dregs of the fusion energy, partly because it takes higher and higher pressures and temperatures for fusion to occur for heavier elements.

When you get to the pressure and temperature points where iron fuses into still heavier elements, it begins to EXTRACT energy - from the core of the star. Stars exist in a delicate balance between the heat and pressure that tries to blow them apart, and the gravity that tries to crush them together. Take heat OUT of the core of the star, and there's less internal pressure - and gravity starts to win. The core will collapse, generally abruptly, and a crushing "rebound effect" will accelerate the heavy fusion, extracting MORE energy, leading to a core collapse supernova. The star explodes, leaving a black hole or pulsar at the center and blasting a lot of the stellar material back into space.

Which is where we got the iron for our blood, or the gold for our jewelry - blasted out of a supernova. Probably MANY of them.

By the way nickel 62 is the ultimate symbol of death, the atom with the most binding energy per nucleon, and not Iron. I had a job where I extracted cobalt from nickel, and I was thinking this is how the world is gonna end, extracting high energy stuff from the low energy nickel 62 waste. Iron 56 is often cited instead of nickel 62, and it's close in binding energy, but not top, and more abundant because of units of 4, alpha radiation of helium atoms predominate as a unit in building up heavier elements, an

Actually the http://en.wikipedia.org/wiki/N... [wikipedia.org] wikipedia page says, even though highest binding energy of all known nuclides per nucleon, Ni 62 per se is very rare, even amongst nickel, because of the difficulty of producing it by neutron capture. Fe 56 has the lowest mass per nucleon, and this whole thing is not a contradiction (lowest mass meaning lowest total energy, or highest binding energy) because when counting nucleons we confuse/confound neutrons with protons. Ni 62 contains a higher ratio of neutr

Also, suppose there was a big bang, and all matter started out as hydrogen at 3 K temperature. What's the equilibrium temperature when all the hydrogen is converted to Ni 62 or Fe 56? It's certainly no longer 3K, unless the conservation of energy does not stand. If there is such a thing as thermal heat death of the Universe as predicted by Thompson, (Lord Kelvin) and the 2nd law of thermodynamics, this equilibrium heat death may be of a very hot temperature, at which not the most stable nuclide would releas

What kenwd0olq said. If you want somewhat more detailed explanation listen to Richard Pogge's excellent Astronomy 162 lecture series and specifically the lectures about death of low and high mass stars (might be somewhere around lectures 14 and 15 but that's just from memory and I'm not sure about that at all).

Um.. but no energy could be released from such a star surely, since fusion of anything heavier than iron produces no energy, but actually takes energy. The only way it could produce energy then would be fission. But I'm skeptical about whether a star in such circumstances would really light up, or would just be a sphere of dead metal.

If I'm reading TFA correctly, it basically means that stars formed from one molecular cloud have very different metallicities - anywhere between the mean metallicity of the molecular cloud and the "purely metal" extreme. If this is actually true, there may be far reaching implications for the research of stellar clusters. One of the basic assumptions in this field is that all cluster stars created from a given molecular cloud have very similar chemical compositions.

In astrophysics, the term "metal" normally applies to any element heavier than lithium. Carbon, silicon, even gasses like oxygen and nitrogen, are "metals". We're not talking about star remnants that are primarily iron or lead or uranium. Gold would be right out.

The star is a fine balance of gravitational attraction that compresses of all its parts to the point of fusion at the center, and the expansion of the star as the pressure of fusing energy at the center wants to expand the star.

At first, hydrogen is converted to helium and that process is so energy-rich that the star doesn't struggle much to hold off the collapsing effect of gravity.

As other elements are converted from one to the other, the fusion process i

How would you spot them? The stellar spectra you mention are visible because of all the energy that a non-metallic star can generate through fusion. But metal stars don't have that energy available. They'll be dim, which affects the distance at which we can spot them. The lack of light also complicates our ability to determine their spectra. So the fraction of metal stars amongst the stars with a known spectrum will be even lower than that 1:10000.